The following main categories can be applied to MPFMs (Multiphase Flow Measurement) and are briefly described in the following Sections:
- Separation type meters
o Full two-phase gas/liquid separation
o Partial separation
o Separation in the sample line
- In-line meters
In-line MPFMs are characterised in that all the measurements of the individual phase fractions and total or individual phase flow rates are performed directly in the multiphase flow line, hence, no separation and/or sampling of the fluids are required.
Some multiphase meters assume that two or all three phases travel at the same speed, which reduces the required number of measurements. In this case, you must use a mixer or set a set of calibration factors
Separation type meters:
Separation type multiphase meters are a class of multiphase meters characterised by performing a complete or partial separation of the multiphase stream, followed by in-line measurement of each of the three phases.
The test separator, which is found on almost all production platforms, is basically a two- or three-phase separation meter. Separate the three phases and carry out oil, water and gas flow measurements. There are three types of separation type meters:
1. Full two-phase gas/liquid separation
This type of meter is characterised by its separation of the multiphase flow, usually a full separation to gas and liquid.
Gas flow is measured using a single phase gas flow meter with good liquid drag tolerance, and the liquid flow rate is measured with a liquid flow meter.
2. Partial separation
In this type of meter is separated only a part of the gas in the multiphase flow into a secondary measurement loop around the main loop through MPFM.
Since the separation is only partial, one should also expect some liquid to travel with the gas through the secondary measuring circuit, which then requires a “wet gas” measurement. The remaining multiphase current will have a reduced GVF and, therefore, will operate within the designed envelope of the flow meter.
3. Separation in sample line
This type of meter is characterised by the fact that separation is not performed on the total multiphase flow, but on a by passed sample flow.
The sample flow is typically separated in a gas and liquid flow, where after the water to liquid ratio of the liquid sample stream can be determined using an in-line water fraction meter. The ratio and the total gas / liquid flow rate should be measured in the main flow line and it is assumed that the voided sample flow is the representation of the main flow.